The sorry looking engine pictured here was purchased with the other bargain hoard of 20 year old aeromodelling planes & accessories. Originally destined to go into the Cambria Pioneer, the gooey coating was a put off, and having flown the plane on a Thunder Tiger GP.15 I am quite sure it would not have had sufficient power to fly this model. I have used this engine for this months project as it would only take an afternoon to complete & this has been a hectic month of off-site activity for those of us at Bumpy Green.

The first time I handled this engine, it was very stiff and covered in fuel residue, both sticky & baked on solid. It was difficult to tell if the little .15 size engine would actually run again but I decided if it wouldn't run it would not look out of place on display somewhere.



The parts laid out above with a 2 pence coin to give an idea how small this engine really is.

Getting the OS to bits was not difficult at all, even though the gummed up head bolts needed a little scrubbing before an allen key could be used. The worst affected areas were the sides of the cylinder head & the exhaust pipe. Even heavy scrubbing could not shift the baked on fuel residue. The engine barrel - piston liner & cooling fins - comes out as one piece & note was made of the direction it faces as the inlet & exhaust ports need to be aligned the right way when reassembling.



Lots of baked on residue under the rim of the cylinder head. The piston liner was still polished & had no pits or scratches so I decided to go ahead with the cleaning process.
Engine dis-assembly steps will be different for each type so I will not list them here but the following cleaning method will be the same for all.

Fill a saucepan (pick a suitably old one that won't be used for cooking again to save self from wrath of kitchen overlord) with enough water to cover the parts, place saucepan on the heat & bring it to the boil.
Next add a few spoons of ordinary washing powder, turn the heat down to simmer so it doesn't boil up & bubble over the sides.

IMPORTANT - Remove all rubber seals & gaskets from the engine as these will be damaged if boiled in water.

Place the engine parts into the saucepan carefully, don't drop them in as splashes of boiling soap water can hurt. Do not leave the engine unattended on the heat as it may boil over as the detergent begins to act on the residue. This may take a little time but keeping an eye on it for 15 minutes is better than half an hour cleaning dried dirty water off the cooker top. Take my word for it.



Boiling nicely after the first wave of foaming was complete. Make sure the water level doesn't drop below the engine parts, the crank case usually being the tallest, as this can leave a tide mark on the sides.



After a while the dirt & grunge begins to float to the top as it lifts from the engine. There is also plenty of it that sinks so be careful where you tip the water away. I used long forceps to fish bits out periodically to check them. The cylinder head needed a little help from an old toothbrush to clear the cooling fins, but that is not hard work as the residue is reduced to sludge at this stage. More soap can be added if required but again watch out for it boiling over.

I found once the water begins to stop foaming the cleaning is done. Keep the water simmering gently and remove the engine parts one at a time & carefully dry them with a cloth. Care must be taken as the parts will still b quite hot & a thick cloth is advised. Don't use toilet roll as it leaves little while specks of fluff all over the engine.

Do no re-assemble the engine whilst the parts are hot, leave them to cool down slowly & completely.

Wiping oil onto the moving parts at this point will ease assembly & prevent and dry friction damage. Parts to consider are the piston & liner, crankshaft & con rod as well as any bearings - both bush & ballrace types - fitted to a particular engine. Never force any parts together, always check and make sure any sliding fit parts are also lubricated - carb & backplate etc. Wipe excess oil from the outside of the engine & double check all bolts are tightened correctly. Remember to refit any gasket or rubber seals that were previously removed.



I used Autosol alloy polishing cream & a small wool polishing brush to bring a 'newer than new' shine back to the engine. This is time consuming & is not essential but it does make the engine stand out nicely (if visible on the model that is.)



Polished & ready for testing. A few squirts of fuel down the carb to get everything moving smoothly, fit a propeller, screw in a glow plug & flick the prop. The OS returned remarkably good compression & I see no reason it will not run well enough to power something small in the coming season ....... I wonder how easily it could be fitted to a Pico-Jet.

Boiling water & hot metal engine parts present certain dangers if not handled safely. Always use common sense & always make sure if anyone is likely to wander in to 'see what's cooking' they are aware of what you are doing. Never leave the boiling pan unattended, if you have to leave it for any reason turn off the heat & move the saucepan to the back of the cooker out of the way.

Never cool the engine parts by placing them in cold water. Certain metal cools & shrinks at a different rate to other metals & materials. This can cause considerable damage especially to alloy crank cases with steel or brass liners. For the same reasons never boil an engine when it is assembled.

Article by Chinman for Bumpy Green Model Aerodrome
1st April 2002